Which situation warrants immediate attention before diving?

Missing diving gear warrants immediate attention because ensuring you have all necessary equipment is crucial for safety while diving. The absence of essential gear, such as a buoyancy control device, regulator, or wetsuit, can significantly increase the risks involved in a dive. Diving without the proper equipment can lead to dangerous situations, including equipment failure or an inability to manage buoyancy and safety during the dive.

On the other hand, light rain, feeling comfortable with the diving conditions, and the lack of divers on the same day do not directly compromise safety in the same way as incomplete gear does. While weather and personal comfort levels can affect a dive, they are not as critical as addressing the necessity of having all your diving equipment ready and in good working order.